Nanoparticle based inks and methods of making the same

ABSTRACT

The present invention provides nanoparticle based recording mediums, inks and ink compositions, methods of making nanoparticle based recording mediums and inks, nanoparticles and methods for making nanoparticles, methods for stabilizing colorants against electromagnetic radiation (including radiation in the visible wavelength range), methods for enhancing the substrate independent durability performance of inks, and methods for color density control. The nanoparticle based inks deliver better color, color density control, improved printability, enhanced durability, and increased lightfastness, and are capable of being printed on woven and non-woven fabrics and paper products without special treatment or other limitations.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to Provisional Application Ser. No.60/237,142, filed Oct. 2, 2000, and Ser. No. 60/243,022, filed Oct. 25,2000, the entirety of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to recording mediums, inks, inkcompositions, methods of making recording mediums and inks,nanoparticles and methods of making nanoparticles.

BACKGROUND OF THE INVENTION

Typically, colorants tend to fade when exposed to electromagneticradiation such as sunlight or artificial light and the like. It isbelieved that most of the fading of colorants when exposed to light isdue to photodegradation mechanisms. These photodegradation mechanismsinclude oxidation or reduction of the colorants depending upon theenvironmental conditions in which the colorant is placed. Fading ofcolorants also depends upon the substrate upon which they reside.

Product analysis of stable photoproducts and intermediates has revealedseveral important modes of photodecomposition. These include electronejection from the colorant, reaction with ground-state or excitedsinglet state oxygen, bond cleavage to form various products, reductionto form colorless leuco dyes and electron or hydrogen atom abstractionto form radical intermediates.

Various factors such as temperature, humidity, gaseous reactants,including O₂, O₃, SO₂, and NO₂, and water soluble, nonvolatilephotodegradation products themselves have been shown to influence fadingof colorants. The factors that effect colorant fading appear to exhibita certain amount of interdependence. It is due to this complex behaviorthat observations for the fading of a particular colorant on aparticular substrate cannot be applied to colorants and substrates ingeneral.

Under conditions of constant temperature it has been observed that anincrease in the relative humidity of the atmosphere increases the fadingof a colorant for a variety of colorant-substrate systems (e.g.,McLaren, K., J. Soc. Dyers Colour, 1956, 72, 527). For example, as therelative humidity of the atmosphere increases, a fiber may swell becausethe moisture content of the fiber increases. This aids diffusion ofgaseous reactants through the substrate structure.

The ability of a light source to cause photochemical change in acolorant is also dependent upon the spectral distribution of the lightsource, that is, the proportion of radiation of wavelengths mosteffective in causing a change in the colorant and the quantum yield ofcolorant degradation as a function of wavelength. On the basis ofphotochemical principles, it might be expected that light of higherenergy (short wavelengths) would be more effective at causing fadingthan light of lower energy (long wavelengths). Studies have revealedthat this is not always the case. Over 100 colorants of differentclasses were studied and found that generally the most unstable werefaded more efficiently by visible light while those of higherlightfastness were degraded mainly by ultraviolet light (McLaren, K., J.Soc. Dyers Colour, 1956, 72, 86).

The influence of a substrate on colorant stability can be extremelyimportant. Colorant fading may be retarded or promoted by chemicalgroups within the substrate. Such groups can be a ground-state speciesor excited-state species. The porosity of the substrate is also animportant factor in colorant stability. A high porosity can promotefading of a colorant by facilitating penetration of moisture and gaseousreactants into the substrate. A substrate may also act as a protectiveagent by screening the colorant from light of wavelengths capable ofcausing degradation.

The purity of the substrate is also an important consideration wheneverthe photochemistry of dyed technical polymers is considered. Forexample, technical-grade cotton, viscose rayon, polyethylene,polypropylene, and polyisoprene are known to contain carbonyl groupimpurities. These impurities absorb light of wavelengths greater than300 nm, which are present in sunlight, and so, excitation of theseimpurities may lead to reactive species capable of causing colorantfading (van Beek, H. C. A., Col. Res. Appl., 1983, 8(3), 176).

In addition to fading, colorants tend to bleed when applied to fabrics.Accordingly, a colorant system that exhibits enhanced stability andcolor fastness when printed or applied to any type of fabric is desired.

What is needed in the art is a colorant system that not only providesincreased light fastness and better color stability, but also one whichis capable of being printed on fabrics without special treatment orother limitations. In addition, a superior textile printing ink withsubstrate independent durability performance is needed. There alsoexists a need for methods and compositions which are capable ofstabilizing a wide variety of colorants from the effects ofelectromagnetic radiation, such as sunlight and artificial light.

SUMMARY OF THE INVENTION

The present invention is directed to, among other things, new recordingmediums, new inks, ink compositions, nanoparticles, methods of makingand using nanoparticles, methods for stabilizing colorants againstphotodecomposition, and methods for stabilizing colorants againstoxidation or reduction. In accordance with the present invention suchrecording mediums, when applied to substrates, exhibit improved waterand detergent resistance. The present invention includes methods forenhancing the substrate independent durability performance of inks andmethods to stabilize colorants against fading due to interactions with asubstrate, as well as methods for color density control. By employing ananoparticle template upon which to bind a colorant and/or chargedpolymer-colorant layer(s), this invention provides new recording mediumsand ways to control their stability, durability and color intensity.

In general, the following discussion relates to particles having adiameter less than about 1,000 nanometers. However, the presentinvention is also directed towards particles having a diameter greaterthan 1,000 nanometers. The present invention is directed to recordingmediums comprising particles or nanoparticles with a colloidal innercore which is used as a particle template surface. One aspect of thepresent invention is multiple, alternating layers of chargedpolymer-colorant (or polyelectrolyte-colorant) being assembled on thenanoparticle template core surface. Because these layers arecharacterized by alternating charges, layer integrity is maintained by avariety of chemical and physical forces, including coulombic forces, vander Waals forces and others. Different colorants may be used insequential charged polymer-colorant layers to afford unusual orhard-to-obtain colors. Additionally, charged polymer-colorant layers mayalternate with layers of charged polymer void of colorant (“void chargedpolymer” layers), in order to protect the colorant below the voidcharged polymer layers, to manipulate particle charge, or to alter itssurface characteristics. Charged polymer layers may also contain“functional additives” such as UV or visible radiation filter moleculesor substances to protect dyes from harmful radiation, leuco dyes orcolorless predyes that develop color upon irradiation, or reactivespecies generators that react to fade colors upon irradiation. A finaloutside layer, comprised of a protective stratum of transparent chargedpolymer, may optionally be added to the nanoparticle. When assembled inthis fashion, the final charge of this protective outer layer (zetapotential) is employed to enhance the adherence of the dye particle tothe fabric surface during printing. Thus, by matching the nanoparticlecharge to the opposite charge of the printing substrate or textilecoating, strong coulombic attraction can be achieved, in addition to vander Waals and other physical and chemical forces. One aspect of thepresent invention includes the nanoparticle comprising a silicaparticle. However, other inorganic nanoparticles as well as organic andorganometallic nanoparticles may be employed herein, the selection ofwhich will be apparent to one of ordinary skill in the relevant art.

The present invention is also directed to nanoparticles that containmore than one colorant and optionally contain colorant stabilizers. Thenanoparticles may comprise a charged polymer membrane or coating whichprevents materials or reactants which might degrade the colorant frominteracting with the colorant. The present invention is directed tonanoparticles with a colloidal inner core that is used as a templatesurface upon which to bind a series of functional layers. Thenanoparticles may be incorporated into a variety of liquid mediums toform colorant compositions, including inks in ink jet processes.

The present invention is further directed to a method of stabilizing acolorant by assembling charged polymer layers, including multiple,alternating layers of charged polymer-colorant and colorless chargedpolymer, on a nanoparticle surface. In one aspect of the presentinvention, one or more colorant stabilizers are also incorporated in thecharged polymer layers, thereby providing multiple levels of colorantprotection from photodegradation mechanisms.

The present invention is also directed to recording mediums containingthe above-described nanoparticles. The recording mediums may be appliedto any substrate to impart a color to the substrate. One aspect of thepresent invention is that, a colorant composition comprising thenanoparticles described above, a liquid medium and a pre-polymer iscoated onto a substrate and subsequently exposed to radiation to fix thenanoparticle to the substrate via the polymerization of the pre-polymer.

Another aspect of the present invention is the above describednanoparticles being present in a polymer coating of a heat transferproduct, such as is used for transferring graphic images onto clothing.

The above described nanoparticles are very effective in ink jet inks.Use of the nanoparticles, as described herein, intensifies the colorsand stabilizes the colorants when they are exposed to light and otherpotentially degrading conditions. Additionally, the nanoparticles areeffective in coatings for paper products and textiles.

These and other features and advantages of the present invention willbecome apparent after a review of the following detailed description ofthe disclosed embodiments.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates one aspect of the present invention, depicting theformation of a nanoparticle by adding multiple layers of chargedpolymer-colorant or alternating layers of chargedpolymer-colorant/colorless charged polymer onto a nanoparticle template.The size of the resulting nanoparticle will increase accordingly, asshown.

FIG. 2. illustrates one aspect of the present invention, depicting theformation of a nanoparticle by adding multiple layers of alternatingcharge of charged polymer-colorant and colorless charged polymer onto acharged silica nanoparticle template. This figure emphasizes thecoulombic forces, in addition to the van der Waals and other physicaland chemical forces, that increase the stability of the nanoparticle,and provide greater colorfastness of the resultant inks.

FIG. 3 illustrates one aspect of the present invention, depicting thechange in zeta potential of a nanoparticle of the present inventionduring its assembly, as sequential, oppositely charged layers of chargedpolymers (with or with colorants associated) are associated with thenanoparticle in a stepwise fashion. The measurements shown are forsilica nanoparticles being layered with a PE(+) ofpoly(2-methacryloxyethyltrimethyl ammonium bromide) with acid red 52associated therewith (layers 1, 3, 5 and 7) and a PE(−) of poly(styrenesulfonic acid, sodium salt) (layers 2, 4, 6 and 8).

DETAILED DESCRIPTION OF THE INVENTION

The following discussion relates to particles having a diameter lessthan about 1,000 nanometers; however, the present invention is alsodirected towards particles having a diameter greater than 1,000nanometers. According to the present invention recording media containnanoparticles with a colloidal inner particle template which is used asa template surface. The nanoparticles, before coating, may have anaverage particle size or diameter of less than about 100 nanometers(nm). In another aspect of the present invention, the average particlesize may be less than about 25 nm. Further, the nanoparticles may havean average size of about 15 nm.

The nanoparticles of the present invention comprise inorganic or organicmaterials, such as aluminum oxide, titanium dioxide, antimony tin oxide,cerium oxide, copper oxide, indium tin oxide, iron oxide, yttrium oxide,zinc oxide, iron oxide, gold, silver, copper, iron, alloys of tin andcopper, carbon (charcoal), sulfur, silicon, fluorosil, a variety oforganic polymers, such as melamine formaldehyde, nylon, polystyrene,polyester, polyamides, combinations thereof, derivatives thereof, orcopolymers thereof. However, in addition to various oxides,nanoparticles may also comprise borides, carbides, silicides, nitrides,phosphides, arsenides, sulfides, selenides, tellurides, fluorides,chlorides, bromides, or iodides, or combinations thereof.

The nanoparticles of the present invention may be any shape, forexample, a sphere, crystal, rod, disc, or tube, depending upon the shapeof the nanoparticle template itself. In one aspect of the presentinvention, the nanoparticles comprise an organic polymer, wherein thenanoparticles are formed in an oil/water system by high shearemulsification. The nanoparticle are characterized by a positive ornegative zeta potential, which is significant in coating thenanoparticle with colorant, charged polymer, functional layers, and/orprotective layers.

The size of the charged polymer-colorant coated nanoparticles variesaccording to the number of alternating layers of chargedpolymer-colorant polymer and charged polymer that are layered on theparticle. In one example, uncoated silica nanoparticles between about 11and about 14 nm in diameter produced layered particles between about 30and about 36 nm in diameter. The diameter of the coated nanoparticle istypically less than about 1000 nm for ink jet compositions, but may beless than about 400 nm, or even less than about 100 nm. Table 1illustrates the increase in the average diameter of the nanoparticleafter being coated with a charged polymer-colorant layer. In Table 1,the positive polyelectrolyte or charged polymer (abbreviated PE(+)) ispolyethylenimine, permethylated, perbromide (MW=1800, Polysciences,Warrington, Pa.), and the negative polyelectrolyte or charged polymer(abbreviated PE(−)) is poly(vinylsulfonic acid, sodium salt) MW=2000,Polysciences, Warrington, Pa.).

TABLE 1 Nanoparticle Size Determination Mean Polyelectrolyte LayerSample Diameter (nm) Thickness (nm) SNOWTEX ™C 10.2 — 0.01MSNOWTEX ™C/PE(+) 15.5 2.6 0.1M SNOWTEX ™C/PE(+) 18.9 4.4 0.01MSNOWTEX ™C/ 51.2 17.9 PE(+)/PE(−) 0.1M SNOWTEX ™C/ 48.2 16.7 PE(+)/PE(−)

FIG. 1 illustrates one aspect of the present invention, namely theformation of a nanoparticle by adding multiple layers of chargedpolymer-colorant or alternating layers of chargedpolymer-colorant/colorless charged polymer onto a nanoparticle template.The size of the resulting colored nanoparticle will increaseaccordingly, as shown. In this figure, charges on the nanoparticle andcharged polymer are not specified.

In one aspect, the nanoparticle of the recording medium has, multiple,alternating layers of charged polymer-colorant and colorless chargedpolymer or “void” charged polymer (without a colorant) layers assembledon the nanoparticle template surface. Another aspect of the presentinvention is multiple, alternating layers of charged polymer-colorantbeing assembled on the nanoparticle template core surface without voidcharged polymer layers between the charged polymer-colorant layers. Inone aspect, different colorants may be used in sequential chargedpolymer-colorant layers to afford tailored colors. The particle templatemay have an initial coating of colorant or other functional additivelayers, prior to coating by a charged polymer or chargedpolymer-colorant layers. Charged polymer layers may also contain“functional additives” such as UV or visible radiation filter moleculesto protect dyes from harmful radiation, leuco dyes or colorless predyesthat develop color upon irradiation, or reactive species generators thatreact to fade colors upon irradiation. Because, in one aspect, layersare characterized by alternating charges, the integrity of the layers ismaintained by coulombic forces, as well as by van der Waals and otherphysical and chemical forces. Changes in the zeta potential after eachlayer confirms substantially uniform and substantially complete coatinghas been achieved. Table 2 illustrates the zeta potential of thenanoparticle following the disposition of sequential chargedpolymer-colorant layers on the particle template. In Table 2, thepositive charged polymer (abbreviated PE(+)) is polyethylenimine,permethylated, perbromide (MW=1800, Polysciences, Warrington, Pa.), andthe negative polyelectrolyte (abbreviated PE(−)) is poly(vinylsulfonicacid, sodium salt) MW=2000, Polysciences, Warrington, Pa.). Eachnumerical column in Table 2, from left to right, represents a successivePE/dye layer being deposited on the nanoparticle, which is oppositelycharged from the underlying layer.

TABLE 2 Zeta Potentials (mV) of Polyelectrolyte (PE)/Dye DepositedSNOWTEX ™C (SNC) PE(−)/ PE(+)/ PE(+)/ PE(+)/ PE (−)/ Sample SNOWTEX ™CSNC SNC PE(+)/SNC Magenta Dye −25 +18 −21 +35 Sulforhodamine BCIBACRON ® −25 +17 −22 +36 Yellow P-6GS Copper −25 +37 −42 +38Phthalocyanine, Tetrasulfonic Acid, Tetra Sodium Salt

A final outside layer, comprised of a protective stratum of transparentcharged polymer, may optionally be added to the nanoparticle. Whenassembled in this fashion, the final charge of this protective outerlayer (zeta potential) is employed to adhere the dye particle to thefabric surface during printing. Thus, by matching the nanoparticlecharge to the opposite charge of the printing substrate or textilecoating, strong coulombic attraction between the nanoparticle and thesubstrate can be achieved, in addition to any other physical andchemical forces that augment this attraction.

FIG. 2. illustrates one aspect of the present invention, that is theformation of a nanoparticle by adding multiple layers of alternatingcharge of charged polymer-colorant and colorless charged polymer onto acharged silica nanoparticle template. Among other things, this figuredemonstrates how the integrity of the layers is maintained by coulombicforces in addition to van der Waals and other physical and chemicalforces, how a final outside layer comprised of a protective stratum ofcharged polymer may be added to the nanoparticle, and how the coulombicand other forces that increase the stability of the colored nanoparticleprovide greater colorfastness of the resultant inks.

FIG. 3 illustrates another aspect of this invention by recording thechange in zeta potential of a nanoparticle during its assembly, assequential, oppositely charged layers of charged polymers (with orwithout colorants associated) are layered onto the nanoparticle in astepwise fashion. The measurements shown are for silica nanoparticlesbeing assembled with a PE(+) of poly(2-methacryloxyethyltrimethylammonium bromide) with acid red 52 associated therewith (layers 1, 3, 5and 7) and a PE(−) of poly(styrene sulfonic acid, sodium salt) (layers2, 4, 6 and 8). We note however, that it is not necessary that ananoparticle that is being formed in this manner exhibit an oppositezeta potential from the polymer charge that is being applied or coatedthereto. Thus, the layer-by-layer self-assembly of simplydifferently-charged polymers (with or without colorant associatedtherewith) may be effected in the same way as assembling a nanoparticlewith alternately-charged layers.

The presence of surface charges on suspended particles, including thenanoparticle template of the present invention, can arise by a varietyof phenomena. Possibilities include the presence of latticeimperfections, various chemical reactions on the surface (e.g.dissociation of functional surface groups), the presence ofsurface-adsorbed ions, and adsorption or dissociation of charge-bearingmolecules. The dissociation of functional surface groups that arecharged and/or adsorption of ions are aspects of the present invention.The surface adsorption of larger molecules containing charged groupssuch as surfactants and charged polymers may also play a role in thepresent invention. The surface charge of the particles is compensated inthe liquid phase by counter ions, thereby ensuring the condition ofelectrical neutrality in the system as a whole.

The strong coulombic and other physical and chemical forces between thenanoparticle and the printing substrate provide enhanced stability,durability, and light fastness. In addition, by alternating colorantlayers with a protective outer layer sheath, light fastness may beenhanced. The ability to coat a nanoparticle with multiple layers alsoallows for color density control.

This layer-by-layer self-assembly of alternately-charged and/ordifferently-charged, charged polymer-colorant polymers (including, insome embodiments, colorless charged polymer) bound to a nanoparticletemplate provides the resulting recording medium or ink with enhancedlight fastness, unlimited use of water soluble dyes (containing chargecenters), control of color density, and strong fabric bonding viacoulombic, van der Waals and other attractive forces leading to enhanceddurability. In addition, control of color density may also be achievedby adjusting reaction times between the nanoparticle substrate and thecharged polymer-colorant where the extent of coating the particledictates color density.

The present invention is also directed to nanoparticles that containmore than one colorant and optionally contain colorant stabilizers. Thenanoparticles comprise a charged polymer membrane or coating whichprevents materials or reactants which might degrade the colorant frominteracting with the colorant.

In addition, the nanoparticles may be incorporated into a variety ofliquid mediums to form colorant compositions. One aspect of the presentinvention is directed towards a nanoparticle comprising ultravioletcolorant stabilizers such as hydroxybenzophenones, benzotriazoles,metalloporphines and triiodophenols.

The present invention is further directed to a method of stabilizing acolorant by assembling multiple, alternating layers ofpolyelectrolyte-colorant and colorless charged polymer on a nanoparticlesurface. One aspect of the present invention includes one or morecolorant stabilizers being incorporated in the charged polymer layers,thereby providing multiple levels of colorant protection fromphotodegradation mechanisms.

The present invention is also directed to recording mediums containingthe above-described nanoparticles. The recording mediums may be appliedto any substrate to impart a color to the substrate. One aspect of thepresent invention involves a recording medium comprising thenanoparticles described above, a liquid medium and a pre-polymer coatedonto a substrate and subsequently exposed to radiation to fix thenanoparticle to the substrate via the polymerization of the pre-polymer.

Another aspect of the present invention involves the above describednanoparticles present in a polymer coating of a heat transfer product,such as is used for transferring graphic images onto clothing.

The above described nanoparticles are very effective in ink jet inks.Use of the nanoparticles, as described herein, intensifies the colorsand stabilizes the colorants when they are exposed to light and otherpotentially degrading conditions. Additionally, the nanoparticles areeffective in coatings for paper products and textiles.

To describe the various aspects of the present invention, the followingdefinitions are provided.

As used herein, the term “colorant” is meant to include, withoutlimitation, any material which typically will provide tint or color to asubstrate. The term is meant to include a single material or a mixtureof two or more materials. Suitable colorants for use in the presentinvention include, but are not limited to, dyes and pigments. Thecolorant can be an organic dye.

A “nanoparticle”, as used herein, refers to nanometer-sized inorganic,organic, or organometallic particles that contain at least one metal ornon-metal element as a component. This definition includes, but is notlimited to, particles of borides, carbides, silicides, nitrides,phosphides, arsenides, oxides, sulfides, selenides, tellurides,fluorides, chlorides, bromides, or iodides, or combinations thereof.This term also encompasses more complex inorganic species such as asingle chemical phase in which more than one metal is combined withanother element (e.g. a bimetallic oxide such as antimony tin oxide orindium tin oxide), a single chemical phase in which a metal is combinedwith more than one other element (e.g. a metal oxycarbide or a metalcarbonitride), derivatives thereof, and combinations thereof innanoparticle form. It is to be understood that metal oxides encompassedby this invention, include but are not limited to, oxides of silicon,aluminum, titanium, zirconium, iron, antimony, tin, cerium, barium,manganese, vanadium, chromium, lead, copper, indium, yttrium, zinc,mixed oxides thereof, and combinations of oxides thereof. A “mixedoxide”, as used herein, describes a single chemical phase in which morethan one metal is combined with oxygen to form a single chemicalcompound. For example, BaTiO₃ and YMnO₃ represents mixed oxides whichare different from mixtures of two oxide compounds, of which anIn₂O₃/SnO₂ mixture is an example. The nanoparticles of the presentinvention also encompass dye or pigment crystallites, either alone orassociated with another nanoparticle of this invention, that can then becoated with charged polymer-colorant layers as described herein.

“Nanoparticle”, as used herein, also encompasses organic-basednanoparticles. This description includes, but is not limited to, polymerparticles, such as particles of polyacetals, polyacetaldehydes,polyacetates, polyacetylenes, polyacrylamides, polyamideimides,polyacrylates, polyacrylic acids, polyacrylonitriles, poly(melamineformaldehyde), polyalkylsilynes, poly(amic acids), polyamides,polycaproic acids, polyanilines, polyaramides, polyarylates,polybenzimidazoles, polybenzothiazones, polybenzoxazoles, polyalkadienes(such as polybutadienes or polypentadienes), polybutenes, poly(alkyleneterphahalates), poly(caprolactams), poly(caprolactones), polycarbonates,polycarbosilanes, polychloroprenes, polyalkylenes (such aspolyethylenes, polypropylenes, and polybutenes), polyalkyleneoxides(such as polyethylene oxides or poly-p-phenyleneoxides),polyalkylenesulfides (such as polyethylene sulfides), polysilanes,polysiloxanes, polysilylenes, polyepichlorohydrins, polyesteramides,polyesters, polyimides, polyethers, polyalkylene glycols, polyglycols,polyether glycols, polyetherimides, polyketones, polysulfones,polyethyleneimines, polyimidosulfides, polyketones, polyisoprenes,polyphosphates, polynitriles, polystyrenes, polyurethanes,polytriazoles, polyterpenes, polynitrides and polysulfides. However, theorganic nanoparticles that are encompassed by the present invention arenot limited to polymer particles, as particles of non-polymeric organicmolecules, oligomers, resins, and mixtures are included herein.

The term “charged polymer” or the term “polyelectrolyte” are, ingeneral, used interchangeably herein to include, without limitation anypolymer or oligomer that is charged. Therefore, this term includes anypolymer comprising an electrolyte, that is, a polymer comprising formalcharges and its associated counter ions, the identity and selection ofwhich will be well known to one of ordinary skill in the art. However,this term is also used to include polymers that can be induced to carrya charge by, for example, adjusting the pH of their solutions. Forexample, the polyelectrolyte poly(butyl acrylate-methacryloxyethyl)trimethylammonium bromide is included in the use of the term “chargedpolymer”, as is the polymerpoly[N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine-co-2,4-dichloro-6-morpholino-1,3,5-triazine]which can readily be protonated so that it becomes charged. Additionalterms “polyelectrolyte-polymer”, “colorless charged polymer”, “colorlesspolyelectrolyte”, “void charged polymer”, “void polyelectrolyte”, or“transparent charged polymer”, and so forth, are used herein to refer toa charged polymer. Charged polymers or polyelectrolytes are abbreviatedPE throughout, and may be designated as positively charged PE(+) ornegatively charged PE(−). Examples of polycations used herein arepolyethyleneimine permethylated perbromide andpoly(2-methacryloxyethyltrimethylammonium bromide). Examples ofpolyanions used herein are poly(vinyl sulfonic acid, sodium salt) andpoly(styrene sulfonic acid, sodium salt).

The terms “charged polymer-colorant” (alternatively, “colorant-chargedpolymer”), “polyelectrolyte-colorant”, “complexed colorant” or similarterms like “complexed dye” are used herein, without limitation, to referto a colorant that is associated, adsorbed, bonded, or complexed in anyway with a charged polymer, including but not limited to, coulombic, vander Waals and other physical and chemical forces.

The term “zeta potential” is used herein to mean without limitation apotential gradient that arises across an interface. This term especiallyrefers to the potential gradient that arises across the interfacebetween the boundary layer in contact with the nanoparticle of thepresent invention and the moveable diffuse layer in which thenanoparticle is suspended. Zeta potential measurements were taken usinga Zetapals Instrument (Brookhaven Instrument Corporation, Holtsville,N.Y.), by adding 1-3 drops of sample into a cuvet containing 1 mM KClsolution, using the instrument's default functions preset for aqueoussolutions.

The term “light-stable” as used herein means, without limitation, thatthe colorant, when associated with a charged polymer which itself isassociated with a nanoparticle, is more stable to electromagneticradiation, including, but not limited to, sunlight or artificial light,than when the colorant is not associated with a nanoparticle.

The term “artificial light” as used herein is meant to mean, withoutlimitation, light having a relatively broad bandwidth that is producedfrom conventional light sources, including, but not limited to,conventional incandescent light bulbs and fluorescent light bulbs.

The term “molecular includant,” as used herein, is intended to mean,without limitation, any substance having a chemical structure whichdefines at least one cavity. That is, the molecular includant is acavity-containing structure. As used herein, the term “cavity” is meantto include any opening or space of a size sufficient to accept at leasta portion of the colorant. Examples of molecular includants include, butare not limited to, the cyclodextrins, which are discussed below.

The term “functionalized molecular includant” as used herein is meant tomean, without limitation, a molecular includant to which one or moremolecules of a colorant stabilizer are covalently coupled to eachmolecule of the molecular includant.

The term “degree of substitution” is used herein to refer to the numberof these molecules or leaving groups (defined below) which arecovalently coupled to each molecule of the molecular includant.

The term “derivatized molecular includant” as used herein is meant toinclude, without limitation, a molecular includant having more than twoleaving groups covalently coupled to each molecule of molecularincludant.

The term “leaving group” as used herein, is meant to mean, withoutlimitation, any chemical group capable of participating in anucleophilic substitution reaction.

Forming Nanoparticle Inks

The present invention is further directed to a method of coatingnanoparticles with colorants. One method of coating the nanoparticles ofthe present invention comprises forming a solution containing a chargedpolymer and a dye (or other colorant), and mixing this chargedpolymer-colorant solution with a colloidal suspension of nanoparticles.Because these layers are characterized by alternating charges, layerintegrity is thereby maintained by coulombic forces, augmented by vander Waals and other physical and chemical forces.

One aspect of the present invention is that the recording mediumcontaining the nanoparticle comprises a silica particle. However, otherinorganic nanoparticles as well as organic and organometallicnanoparticles may be employed herein, the selection of which will beapparent to one of ordinary skill in the relevant art.

As discussed in the examples below, a silica nanoparticle which can beemployed in the present invention is commercially available as acolloidal suspension known as SNOWTEX™ (Nissan Chemical AmericaCorporation). For example, SNOWTEX™ C is characterized by a silicaparticle size from about 11 to about 14 nm in diameter. Many otherparticles of various shapes may be used as templates in the presentinvention, the selection of which will be apparent to one of ordinaryskill in the relevant art. For example, the nanoparticle can beinorganic (e.g. silica) or organic (e.g. poly(methylstyrene). In oneembodiment, the nanoparticle core can comprise melamine resin(poly(melamine formaldehyde)) nanoparticles. Another embodiment of thepresent invention comprises a nanoparticle core of a preformed organicpolymer that is dissolved in an organic solvent, and high shearemulsification in an oil/water system results in nanoparticle formation.The resultant nanoparticles are then coated with charged polymer layers,in which some of the charged polymer has a dye complexed with it. Theresultant polymer nanoparticles may also be coated with charged polymerlayers comprising different dyes associated with the charged polymer toachieve fine control over color and hue.

In another aspect of this invention, a final protective stratum ofcolorless charged polymer, may be added to the nanoparticle after it hasbeen coated with alternating charged polymer-colorant, and colorlesscharged polymer layers.

Suitable colorants for use in the present invention include, but are notlimited to, dyes and pigments. The colorant may be an organic dye.Organic dye classes include, by way of illustration only, triarylmethyldyes, such as Malachite Green Carbinol base{4-(dimethylamino)-α-[4-(dimethylamino)phenyl]-α-phenyl-benzene-methanol},Malachite Green Carbinol hydrochloride{N-4-[[4-(dimethylamino)phenyl]phenyl-methylene]-2,5-cyclohexyldien-1-ylidene]-N-methyl-methanaminiumchloride or bis[p-(dimethylamino)phenyl]phenylmethylium chloride}, andMalachite Green oxalate{N-4-[[4-(dimethylamino)-phenyl]-phenylmethylene]-2,5-cyclohexyldien-1-ylidene]-N-methyl-methanaminiumchloride or bis[p-(dimethylamino)-phenyl]phenylmethylium oxalate};monoazo dyes, such as Cyanine Black, Chrysoidine [Basic Orange 2;4-(phenylazo)-1,3-benzenediamine monohydrochloride], Victoria Pure BlueBO, Victoria Pure Blue B, basic fuschin and β-Naphthol Orange; thiazinedyes, such as Methylene Green, zinc chloride double salt[3,7-bis(dimethylamino)-6-nitrophenothiazin-5-ium chloride, zincchloride double salt]; oxazine dyes, such as Lumichrome(7,8-dimethylalloxazine); naphthalimide dyes, such as Lucifer Yellow CH{6-amino-2-[(hydrazino-carbonyl)amino]-2,3-dihydro-1,3-dioxo-1H-benz[de]iso-quinoline-5,8-disulfonicacid dilithium salt}; azine dyes, such as Janus Green B{3-(diethylamino)-7-[[4-(dimethyl-amino)phenyl]azo]-5-phenylphenaziniumchloride}; cyanine dyes, such as Indocyanine Green {Cardio-Green or FoxGreen;2-[7-[1,3-dihydro-1,1-dimethyl-3-(4-sulfobutyl)-2H-benz[e]indol-2-ylidene]-1,3,5-heptatrienyl]-1,1-dimethyl-3-(4-sulfobutyl)-1H-benz[e]indoliumhydroxide inner salt sodium salt}; indigo dyes, such as Indigo {IndigoBlue or Vat Blue 1;2-(1,3-dihydro-3-oxo-2H-indol-2-ylidene)-1,2-dihydro-3H-indol-3-one};coumarin dyes, such as 7-hydroxy-4-methyl-coumarin(4-methylumbelliferone); benzimidazole dyes, such as Hoechst 33258[bisbenzimide or2-(4-hydroxyphenyl)-5-(4-methyl-1-piperazinyl)-2,5-bi-1H-benzimidazoletrihydro-chloride pentahydrate]; paraquinoidal dyes, such as Hematoxylin{Natural Black 1;7,11b-dihydrobenz[b]-indeno[1,2-d]pyran-3,4,6a,9,10(6H)-pentol};fluorescein dyes, such as Fluoresceinamine (5-aminofluorescein);diazonium salt dyes, such as Diazo Red RC (Azoic Diazo No. 10 or FastRed RC salt; 2-methoxy-5-chlorobenzenediazonium chloride, zinc chloridedouble salt); azoic diazo dyes, such as Fast Blue BB salt (Azoic DiazoNo. 20; 4-benzoylamino-2,5-diethoxy-benzene diazonium chloride, zincchloride double salt); phenylenediamine dyes, such as Disperse Yellow 9[N-(2,4-dinitro-phenyl)-1,4-phenylenediamine or Solvent Orange 53];diazo dyes, such as Disperse Orange 13 [Solvent Orange 52;1-phenylazo-4-(4-hydroxyphenylazo)-naphthalene]; anthra-quinone dyes,such as Disperse Blue 3 [Celliton Fast Blue FFR;1-methylamino-4-(2-hydroxyethylamino)-9,10-anthraquinone], Disperse Blue14 [Celliton Fast Blue B; 1,4-bis(methylamino)-9,10-anthraquinone], andAlizarin Blue Black B (Mordant Black 13); trisazo dyes, such as DirectBlue 71 {Benzo Light Blue FFL or Sirius Light Blue BRR;3-[(4-[(4-[(6-amino-1-hydroxy-3-sulfo-2-naphthalenyl)azo]-6-sulfo-1-naphthalenyl)-azo]-1-naphthalenyl)azo]-1,5-naphthalenedisulfonicacid tetrasodium salt}; xanthene dyes, such as 2,7-dichloro-fluorescein;proflavine dyes, such as 3,6-diaminoacridine hemisulfate (Proflavine);sulfonaphthalein dyes, such as Cresol Red (o-cresolsulfonaphthalein);phthalocyanine dyes, such as Copper Phthalocyanine {Pigment Blue 15;(SP-4-1)-[29H,31H-phthalocyanato(2-)-N²⁹,N³⁰,N³¹,N³²]-copper};carotenoid dyes, such as trans-β-carotene (Food Orange 5); carminic aciddyes, such as Carmine, the aluminum or calcium-aluminum lake of carminicacid(7-a-D-glucopyranosyl-9,10-dihydro-3,5,6,8-tetrahydroxy-1-methyl-9,10-dioxo-2-anthracene-carbonylicacid); azure dyes, such as Azure A[3-amino-7-(dimethylamino)phenothiazin-5-ium chloride or7-(dimethyl-amino)-3-imino-3H-phenothiazine hydrochloride]; and acridinedyes, such as Acridine Orange [Basic Orange 14;3,8-bis(dimethylamino)acridine hydrochloride, zinc chloride double salt]and Acriflavine (Acriflavine neutral; 3,6-diamino-10-methylacridiniumchloride mixture with 3,6-acridine-diamine).

Suitable colorants for use in the present invention also include afamily of subphthalocyanine compounds having the following generalformula:

wherein R₁ to R₁₂ and Z each independently represent —H; a halogen; analkyl group; a substituted alkyl group; an aryl group; a substitutedaryl group; an alkoxide group; a phenoxy group; a substituted phenoxygroup; an alkyl sulfide; an aryl sulfide; a nitrogen-containing group; asulfonic acid; a sulfur-containing group; —OR′, —NR′R″, or —SR′, whereinR′ and R″ each independently represent an alkyl group, a substitutedalkyl group, an aryl group, or a substituted aryl group. In accordancewith the present invention, R₁ to R₁₂ each independently represent —H, ahalogen, an alkyl group, a nitrogen-containing group, or asulfur-containing group. Typically, R₁ to R₁₂ each independentlyrepresent —H, chlorine, bromine, fluorine, iodine, a tert-butyl group,—NO₂, —SO₃H, —SO₃Na, —SO₃Cl, or —SO₃Cl⁻pyH⁺.

Suitable Z substituents may be selected from a variety of substituents,which provide desirable properties to the resulting subphthalocyaninecompound. In accordance with the present invention, Z may comprise amoiety, which stabilizes the subphthalocyanine compound; a moiety, whichrenders the subphthalocyanine compound water soluble; or a moiety, whichstabilizes and renders the subphthalocyanine water soluble. Examples ofsuitable Z include, but are not limited to, a hydroxyl group; a halogen;an alkyl group; an alkoxy group; an ether group; a polyol group; anaromatic group; a substitute aromatic group; a nitrogen-containinggroup; a sulfur-containing group; —OR′, —NR′R″, or —SR′, wherein R′ andR″ each independently represent an alkyl group, a substituted alkylgroup, an aryl group, or a substituted aryl group. Typically, Z isselected from—though not limited to—one of the following moieties:

where x is an integer from 3 to 30, and R′″ is a hydrogen or an alkylgroup having up to six carbon atoms.

By selecting particular “R” and “Z” groups, subphthalocyanine compoundshaving superior lightfastness properties are available. In oneembodiment of the present invention, subphthalocyanine compounds havingsuperior lightfastness properties are used. In these subphthalocyaninecompounds given by the above-described general formula, R₁ to R₁₂ eachindependently represent —H or a halogen; and Z represents a halogen,—OR′, —NR′R″, or —SR′, wherein R′ and R″ each independently represent analkyl group, a substituted alkyl group, an aryl group, or a substitutedaryl group.

Subphthalocyanine compounds suitable for use in the present inventioninclude, but are not limited to, the following compounds given below,wherein

and wherein abbreviations such as R₁₋₄ represent the substituents R₁ toR₄:

In a further aspect of the present invention, two subphthalocyaninecompounds are reacted with a third reactant to obtain a colorantcompound having the following general formula:

wherein R₂₁ to R₃₆, Z₁, and Z₂ each independently represent moieties asdescribed above with respect to R₁ to R₁₂ and Z. In the formation of theabove compound, the third reactant may be selected from1,3,4,6-tetracyanobenzene or 1,3,4,6-tetracyanobenzene furthersubstituted with one or more electron-withdrawing groups, E₁ and E₂.Suitable electron-withdrawing groups include, but are not limited to,—NO₂.

In a further aspect of the present invention, the lightfastnessproperties of the subphthalocyanine dye may be greatly improved toarchival levels by the presence of a perfluoroporphine. The presentinvention encompasses both the physical mix and the covalent attachmentof the perfluoroporphine and the subphthalocyanine dye. For example,when the subphthalocyanine dye shown below (where R₁ to R₁₂ are H, and Zis —O-3,5-C₆H₃Me₂) is physically admixed withcopper-meso-perfluorotetraphenylporphine (abbreviated CuF₂₀TPP) in apolymer matrix, the absorption (λ_(MAX)) of the subphthalocyanine dyedid not change even after exposure for 10 hours to radiation from anAtlas Suntest CPS+ xenon lamp. Thus, this invention encompasses both theadmixture of subphthalocyanine dye and perfluoroporphine such asCuF₂₀TPP and the covalent attachment of these moieties.

The covalent attachment of the perfluoroporphine and thesubphthalocyanine dye moieties is represented by the complex shownabove, wherein Z comprises a copper-meso-perfluorotetraphenylporphineand a “linker” between the subphthalocyanine dye portion of the moleculeand a phenyl ring of porphine. Therefore, in this example, Z canrepresent —NXCuF₁₉TPP, —PXCuF₁₉TPP, —AsXCuF₁₉TPP, —BXCuF₁₉TPP,—OCuF₁₉TPP, —SCuF₁₉TPP, —CX₂CuF₁₉TPP, —SiX₂CuF₁₉TPP, —GeX₂CuF₁₉TPP,—SnX₂CuF₁₉TPP, and the like, where X can independently represent H,alkyl, aryl, halide, alkenyl, cycloalkyl, heterocycloalkyl, aryl,heteroaryl, alkoxide, phenoxide, substituted derivatives thereof, and soforth. These complexes are prepared by synthetic methods known to one ofordinary skill in the art. For example, the complex in which Z is—NHCuF₁₉TPP was synthesized by reacting the bromo subphthalocyanine withthe amino derivative of the perfluoroporphine to obtain thesubphthalocyanine-NHCuF₁₉TPP compound.

The above-described subphthalocyanine compounds may be used as acolorant, alone or in combination with one or more other colorants. Thesubphthalocyanine compounds may be incorporated into ink compositions,which may form an ink set including yellow, blue, black, and magentainks.

The present invention also relates to colorant compositions havingimproved stability, wherein the colorant comprises one or more of theabove-described subphthalocyanine compounds. In accordance with thepresent invention, one or more of the subphthalocyanine colorants areadmixed with or covalently bonded to a colorant stabilizer. The colorantstabilizer may be one or more colorant stabilizers disclosed in thefollowing U.S. patent application Ser. Nos. 08/563,381 filed Nov. 28,1995, now abandoned; 08/589,321 filed Jan. 22, 1996, pending; and08/788,863 filed Jan. 23, 1997, pending; and U.S. Pat. Nos. 5,782,963;5,855,655; 5,885,337; and 5,891,229; all of which are assigned toKimberly-Clark Worldwide, Inc., the entirety of which are incorporatedherein by reference. Optionally, the new subphthalocyanine compounds maybe associated with a molecular includant, chelating agent, or othermaterial to improve solubility and/or interaction of thesubphthalocyanine compound and any colorant stabilizers present.Suitable molecular includant, chelating agent, and other compositionmaterials are also disclosed in the above-referenced U.S. patentapplications and issued patents.

One aspect of the present invention involves the above-describedsubphthalocyanine compound covalently bonded to a colorant stabilizer inthe form of a porphine. Suitable porphines are disclosed in theabove-referenced in the above cited U.S. patent applications and issuedpatents. In accordance with this aspect of the present invention, theporphine is covalently bonded to the subphthalocyanine compound at Z,Z₁, and/or Z₂. In a further embodiment of the present invention, twosubphthalocyanine compounds are covalently bonded to one another. Inthis aspect, it is typical for one subphthalocyanine compound to bebonded to the other subphthalocyanine compound at Z, Z₁ and/or Z₂.

In one aspect of the present invention, one or more colorant stabilizersare associated with the colorant. By incorporating one or more colorantstabilizers into the solution described above, colorant stabilizers maybe associated with the charged polymer along with the colorant. Suitablecolorant stabilizers for use in the present invention include, but arenot limited to, colorant stabilizers disclosed in the above-cited U.S.patent applications and issued patents.

In a further embodiment of the present invention, suitable colorantstabilizers include, but are not limited to, a porphine, a metal, ametal salt, a molecular includant or a combination thereof.

Suitable porphines include, but are not limited to, porphines having thefollowing structure:

wherein R is any proton-donating moiety and M is iron, cobalt or copper.Typically, R is SO₃H,

COOH, R₁COOH wherein R₁ is an alkyl group of from 1 to 6 carbons, or thecorresponding salt thereof.

In accordance with the present invention, the colorant stabilizer isrepresented by one or more porphines such asCu-meso-tetra-(4-sulfanatophenyl)-porphine (designated CuTPPS4) andCu-meso-tetra-(N-methyl-4-pyridyl)-porphine (designated CuTMPS4), havingthe following structure:

In the above-described porphines, the copper ion can also be substitutedwith an iron or cobalt ion. It is also understood that in the case ofFeTPPS4, CuTPPS4 or CoTPPS4, the sulfuric acid moieties may besubstituted with salts when in solution, such as sodium salts.

In another aspect of the present invention, the nanoparticles comprise acolorant and a colorant stabilizer in the form of a metal or metal salt,such as a lanthanide or lanthanide salt. Although lanthanides andlanthanide salts are useful metals, other metals, may also be used suchas magnesium, iron, zinc, and other transition metals. To improve thesolubility of the metal or metal salt in solution, metalsolubility-enhancing agents may be added. Useful metalsolubility-enhancing agents include, but are not limited to, chelatingagents, including, but not limited to, EDTA (ethylenediaminetetraaceticacid) or EGTA (ethylene glycol-bis(β-aminoethyl ether)).

In a further aspect of the present invention, the nanoparticles comprisea colorant in combination with a porphine and a lanthanide, such aseuropium. Although europium and europium salts are desired lanthanides,other lanthanides, may also be used.

Although not wanting to be limited by the following hypothesis, it istheorized that, in addition to the protection provided by the polymericcoating on the nanoparticle, the above colorant stabilizing compoundsact by quenching the excited state of a dye molecule within thenanoparticle by efficiently returning it to a ground state. Thisquenching process reduces the likelihood of an oxidative or otherchemical reaction occurring which would render the dye chromophorecolorless.

The quenching effect can occur by a number of processes. One suchprocess is referred to as the heavy atom effect (internal or external)in which atoms with a high atomic number, such as iodine, xenon andlanthanides, can effect the excited electronic transitions of the dyemolecule by allowing here to fore forbidden electronic transitions tooccur and by decreasing the excited state lifetimes. This effect permitsthe rapid return of the dye to its ground state.

Another quenching process involves back electron transfer. In this case,quenching of the excited dye molecule occurs through sequential electrontransfer. The additive or quencher, and dye form an ion pair throughelectron donation within which back electron transfer leads to anoverall deactivation of the excited energy donor, i.e., the dye.

Another quenching process involves a condition in which the quencher(additive) molecule has an excited energy state lower than the exciteddye. In this case, it may be possible to transfer the excited energy tothe quencher thereby allowing the dye molecule to return to its groundstate. These mechanisms are more fully discussed in Chemistry and Light,Suppan, P., Published by The Royal Society of Chemistry, 1994, pgs 65-69which is incorporated herein by reference.

In some aspects of the present invention, the colorant and/or colorantstabilizer of the nanoparticle is associated with a molecular includant.The term “associated” in its broadest sense means that the colorantand/or colorant stabilizer is at least in close proximity to themolecular includant. For example, the colorant and/or colorantstabilizer may be maintained in close proximity to the molecularincludant by hydrogen bonding, van der Waals forces, or the like.Alternatively, the colorant and/or colorant stabilizer may be covalentlybonded to the molecular includant, although this normally is neitherdesired nor necessary. As a further example, the colorant and/orcolorant stabilizer may be at least partially included within the cavityof the molecular includant.

The molecular includant can be inorganic or organic in nature. Incertain instances, the chemical structure of the molecular includant isadapted to form a molecular inclusion complex. Examples of molecularincludants are, by way of illustration only, clathrates or intercalates,zeolites, and cyclodextrins. Examples of cyclodextrins include, but arenot limited to, α-cyclodextrin, β-cyclodextrin, γ-cyclodextrin,δ-cyclodextrin, hydroxypropyl β-cyclodextrin, hydroxyethylβ-cyclodextrin, hydroxyethyl α cyclodextrin, carboxymethyl αcyclodextrin, carboxymethyl β cyclodextrin, carboxymethyl γcyclodextrin, octyl succinated α cyclodextrin, octyl succinated βcyclodextrin, octyl succinated γ cyclodextrin and sulfated βcyclodextrin and sulfated γ-cyclodextrin (Cerestar U.S.A., Incorporated,Hammond, Ind.).

The term “derivatized cyclodextrin” as used herein means a cyclodextrinhaving more than two leaving groups covalently coupled to each moleculeof cyclodextrin. Examples of derivatized cyclodextrin includes, but isnot limited to, hydroxypropyl β-cyclodextrin, hydroxyethylβ-cyclodextrin, hydroxyethyl α cyclodextrin, carboxymethyl αcyclodextrin, carboxymethyl β cyclodextrin, carboxymethyl γcyclodextrin, octyl succinated α cyclodextrin, octyl succinated βcyclodextrin, octyl succinated γ cyclodextrin and sulfated β andγ-cyclodextrin. A useful derivatized cyclodextrin is ethylhydroxyβ-cyclodextrin.

Useful molecular includants include, but are not limited toγ-cyclodextrin and β-cyclodextrin. In other embodiments, the molecularincludant is an ethyl hydroxy β-cyclodextrin. Although not wanting to bebound by the following hypothesis, it is believed that the molecularincludant inhibits the aggregation of the colorant molecule in solution.Other aggregation inhibitors that can be used in practicing the presentinvention are starches, pectins, amyloses, clathrates and the crownethers. It is to be understood that the addition of derivatizedcyclodextrins to a coated nanoparticle-forming solution for the purposeof inhibiting aggregation and/or stabilizing the dyes in the coatednanoparticle is considered one aspect of the present invention.

In addition to the colorant, optional colorant stabilizer, and optionalmolecular includant, the nanoparticle of the present invention also maycontain functional additives components, depending upon the applicationfor which it is intended, as long as the additional component does notnegatively effect the dye molecule. Examples of such additionalcomponents include, but are not limited to, leuco dyes, charge carriers;stabilizers against thermal oxidation; viscoelastic propertiesmodifiers; cross-linking agents; plasticizers; charge control additivessuch as a quaternary ammonium salt; flow control additives such ashydrophobic silica, zinc stearate, calcium stearate, lithium stearate,polyvinylstearate, and polyethylene powders; fillers such as calciumcarbonate, clay and talc; surfactants; chelating agents; and TINUVIN®compounds; among other additives used by those having ordinary skill inthe art. Charge carriers are well known to those having ordinary skillin the art and typically are polymer-coated metal particles. Usefulsurfactants include, but are not limited to, C₁₂ to C₁₈ surfactants suchas cetyl trimethyl ammonium chloride and carboxymethylamylose. TINUVIN®compounds are a class of compounds produced by Ciba-Geigy Corporation,which includes benzophenones, benzotriazoles and hindered amines. UsefulTINUVIN® compounds include, but are not limited to,2-(2′-hydroxy-3′-sec-butyl-5′-tert-butylphenyl)-benzo-triazole,poly-(N-β-hydroxyethyl-2,2,6,6-tetramethyl-4-hydroxy-piperidyl succinateand 2-(2′-hydroxy-3′,5′-ditertbutylphenyl)-5-chloro-benzotriazole. Theidentities and amounts of such additional components in the coloredcomposition are well known to one of ordinary skill in the art.

Another aspect of the present invention is directed towards therecording medium of the present invention containing a nanoparticlehaving a surface modifier or surface gloss modifying agent disposed uponthe particle template. Examples of such surface modifiers includepolyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol,chitosans, polysiloxanes, polyacrylic acid, polysiloxane polyethyleneoxide copolymer, polysiloxane polypropylene oxide copolymer, lineardextrins, cyclodextrins, combinations thereof, or copolymers thereof.The addition of the surface modifiers results in a surface with enhancedproperties, such as glossy, matte, dull or textured finishes.

Examples of Applications for Nanoparticle Based Inks

The present invention is also directed to colorant compositionscontaining the above-described nanoparticles. The colorant compositionmay comprise an aqueous or non-aqueous medium, although an aqueousmedium is useful for applications which employ liquid printing mediums.The colorant compositions of the present invention containnanoparticles, as well as, any of the above-described colorantstabilizers and additives. For example, the colorant composition maycontain the above-described nanoparticle in combination with any of thefollowing additives: a second colorant; a colorant stabilizer, such as aporphine; a molecular includant; a pre-polymer; and any additionalcomponents as described above.

The present invention encompasses recording mediums such as ink jet inkscomprising the nanoparticles disclosed herein. Inks used in ink jetprinters are described in U.S. Pat. No. 5,681,380, assigned toKimberly-Clark Worldwide, Inc., which is incorporated herein byreference in its entirety. Ink jet inks will usually contain water asthe principal solvent, preferably deionized water in a range of betweenabout 20 to about 95 percent by weight, various co-solvents in an amountof between about 0.5 and about 20 percent by weight, and thenanoparticles of the present invention.

Various co-solvents may also be included in the ink formulation.Examples of such co-solvents include a lactam such asN-methylpyrrolidone. However, other examples of optional co-solventsinclude N-methylacetamide, N-methylmorpholine-N-oxide,N,N-dimethylacetamide, N-methyl formamide,propyleneglycol-monomethylether, tetramethylene sulfone, andtripropyleneglycolmonomethylether. Still other solvents which may beused include propylene glycol and triethanolamine (TEA). If anacetamide-based cosolvent is also included in the formulation it istypically present at about 5 percent by weight, within a range ofbetween about 1.0-12 percent by weight.

Optionally, one or more humectants in an amount between about 0.5 and 20percent by weight may be included in the ink formula. Further, otherco-solvents in an amount of between about 1.0 and about 7.0 percent byweight may be added to the formulation. Additional humectants foroptional use in the formulation include, but are not limited to,ethylene glycol, diethylene glycol, glycerine, and polyethylene glycol200, 400, and 600, propane 1,3 diol, other glycols, apropyleneglycolmonomethyl ether, such as Dowanol PM (Gallade ChemicalInc., Santa Ana, Calif.), polyhydric alcohols, or combinations thereof.

Other additives may also be included to improve ink performance, such asa chelating agent to sequester metal ions that could become involved inchemical reactions that could spoil the ink over time, for example foruse with metal complex dyes, a corrosion inhibitor to help protect metalcomponents of the printer or ink delivery system, a biocide or biostatto control unwanted bacterial, fungal, or yeast growth in the ink, and asurfactant to adjust the ink surface tension. However, the use of asurfactant may be dependent on the type of printhead to be used. If asurfactant is included, it is typically present in an amount of betweenabout 0.1 to about 1.0 percent by weight. If a corrosion inhibitor isincluded, it is typically present in an amount between about 0.1 andabout 1.0 percent by weight. If a biocide or biostat is included, it istypically present in an amount between about 0.1 and about 0.5 percentby weight.

If a biocide or biostat is added to the ink formulation, it may beexemplified by Proxel GXL (Zeneca Corporation, Wilmington, Del.). Otherexamples include Bioban DXN (Angus Chemical Company, Buffalo Grove,Ill.). If a corrosion inhibitor is added to the formulation, it may beexemplified by Cobratec (PMC Specialty Group Distributing of Cincinnati,Ohio). Alternate corrosion inhibitors include sodium nitrite,triethanolamine phosphate, and n-acyl sarcosine. Still other examplesinclude benzotriazole (Aldrich Chemical Company, Milwaukee, Wis.). If asurfactant is included in the formulation, it is typically a nonionicsurfactant exemplified by Surfynol 504 (Air Products and Chemicals,Inc., Allentown, Pa.). Still other examples include Surfynol 465, andDynol 604 also available from Air Products. If a chelating agent isincluded in the formulation it may be exemplified by an ethylenediaminetetraacetic acid (EDTA). Other additives such as pHstabilizers/buffers, (such as citric acid and acetic acid as well asalkali metal salts derived therefrom), viscosity modifiers, anddefoaming agents such as Surfynol DF-65, may also be included in theformulation, depending on the product application.

The recording media or colorant compositions of the present inventionmay be applied to any substrate to impart a color to the substrate. Thesubstrates to which the nanoparticles may be applied include, but arenot limited to, paper, wood, a wood product or composite, woven fabric,nonwoven fabric, textile, plastic, glass, metal, human skin, animalskin, leather and the like. Examples of suitable substrates aredisclosed in the U.S. patent applications and issued patents citedabove. In one aspect of the present invention, nanoparticles are appliedto a textile article, such as clothing. A very thin coating having athickness of about one nanoparticle may be applied to a textile surface.

In a representative laboratory laundering experiment, a small (about 1inch by 2 inch) piece of fabric of various materials was treated withthe colorant suspension of the present invention. Typically, the samplewas immersed in a suspension of the colorant for 15-20 seconds, removedfrom the colorant and rinsed well with water, and dried under vacuum atambient temperature. The dry, colored sample of fabric was thensubjected to the AATCC (American Association of Textile Chemists andColorists) 61-2A accelerated laundering test. The AATCC 61-2A test forevaluating colorfastness should show color change similar to thatproduced by five commercial launderings at 38±3° C. (100±5° F.) or byfive home machine launderings at medium or warm setting in this sametemperature range. The fabric sample was washed in 150 mL of water at49° C. (120° F.) with 0.25% SYNTHRAPOL™ detergent, along with 50 (0.6cm) steel ball bearings. Wash time was 45 min, in a canister beingrotated at a rate of 40 rpm. The laundered sample was then washed withwater and dried, and the color change and color staining weredetermined.

Two methods of determining the durability of the printed ink by colorloss were employed. The first method is color loss in ΔE* units, whichmeasures the spectroscopic change in the 3D color space. The secondmethod is color loss using a gray scale for color change, which is avisible comparison with color standards. The first (ΔE*) method measuresthe change in the 3D color space, it is generally considered a moreaccurate measurement of the loss of color than the second method.However, the second (gray scale) method is used extensively in thefabric industry.

The color loss by the ΔE* method involves L*a*b* color valuesmeasurements (CIE 1976 Commission Internationale de l'Eclairage) andoptical density measurements which were made on the printed textilesubstrates using an X-Rite 938 Spectrodensitometer (D65/10°) using CMYfilters, in accordance with the operator's manual. The X-RiteSpectrodensitometer was obtained from the X-Rite Corporation ofGrandville, Mich. Average optical densities were taken as the sum of theaverage of three measurements using each filter. Delta E* is calculatedin accordance with the following equation:

ΔE*=SQRT[(L*standard−L*sample)²+(a*standard−a*sample)²+b*standard−b*sample)²]

The higher the ΔE*, the greater the change in color intensity. Unlessthe color's intensity is increased by a curing step, a large increase inΔE* would typically be indicative of fading. The testing was inaccordance with ASTM DM 224-93 and ASTM E308-90. Where values for ΔE*are less than 3.0, it is generally accepted that such color changecannot be observed with the human eye. A detailed description ofspectrodensitometer testing is available in Color Technology in theTextile Industry, 2^(nd) Edition, Published 1997 by AATCC (AmericanAssociation of Textile Chemists & Colorists).

Color loss using a gray scale constitutes an AATCC Gray Scale which isused in visual evaluations of the changes in color of textiles resultingfrom colorfastness tests. Gray Scale color loss is graded between 1(much changed or heavily stained) and 5 (negligible color change or nochange or staining). According to AATCC, the colorfastness grades of thescale steps and the corresponding total color differences and tolerancesused are determined by the CIE L*a*b* (CIELAB) formula. Colorfastnessgrade 5 is represented on the scale by two reference chips mounted sideby side, neutral gray in color and having a Y tristimulus value of12+0.2. Colorfastness grades 4.5 to 1, inclusive, are represented byreference chips like those used in Step 5 paired with lighter neutralgray chips of similar dimensions and gloss. Specific tolerances andinstructions for use of the scale are given in AATCC EvaluationProcedure 1. The Gray Scale for Color Change is used in allcolorfastness tests; including AATCC Test Methods 6, 8, 15, 16, 23, 61,101, 104, 106, 107, 109, 116, 117, 119, 120, 125, 126, 129, 131, 132,133, 139, 157, 162, 163, 164, 165, 172, 173, 177, 180, 181.

Additionally, some printed fabrics were examined for their colorfastnessto crocking, by the rotary vertical crockmeter method (AATCC Test Method116-1996). This test method, according to the AATCC standard, isdesigned to determine the amount of color transferred from the surfaceof colored textile materials to other surfaces by rubbing. It isapplicable to textiles made from all fibers in the form of yarn orfabric, whether the textile is dyed, printed or otherwise colored andespecially to prints where the singling out of areas smaller thanpossible to test with the standard AATCC Crockmeter (AATCC Test Method8) is required. Thus, test procedures employing test squares of printedtextile, whether dry or wet with water or other liquids are within thescope of this method. In this test, a test specimen held at the base ofthe Rotary Vertical Crockmeter is rubbed with standard test squaresunder controlled conditions. Subsequently, color transferred to the testsquares is assessed by comparison with the Gray Scale for Staining orAATCC Chromatic Transference Scale.

Table 3 records the results of the AATCC 61-2A accelerated launderingtest for various fabric samples and colorants of the present invention,as compared to unlaundered samples, with Gray Scale color changemeasured on untreated cotton fabric. Samples 1 (“70-4M magenta”) and 2(“70-3M magenta”) constitute fabric printed with melamine resinnanoparticles coated with rhodamine B dye (magenta), that differ only inthe ink composition (e.g. surfactants) and not the nanoparticles. Thus,70-4M used 1,3-propanediol (neutral), while 70-3M used a 50:50 mixtureof 1,3-propanediol and N,N-dimethyl-morpholine N-oxide (charged). Thus,highly polar ink additives are less useful than only slightly polaradditives. Sample 3 is silica (SNOWTEX™ C) with a CIBACRON® yellow P-6GSdye-PE(+) coating. The magenta nanoparticles (melamine resin coated withrhodamine B) have a positive zeta potential, while the yellownanoparticles (silica coated with CIBACRON® yellow P-6GS dye-PE(+)) havea negative zeta potential (−11 mV), as evidenced by the greaterlightfastness of the magenta particles adhering to cotton fabric with anegative streaming potential.

TABLE 3 Gray Scale Colorfastness by Grade to AATCC 61-2A AcceleratedLaundering Sample 1 Color Change 3.5 Color Staining Acetate 4.5 Cotton 4Nylon 3 Polyester 3.5 Acrylic 4.5 Wool 4 Sample 2 Color Change 3 ColorStaining Acetate 5 Cotton 3.5 Nylon 3.5 Polyester 3.5 Acrylic 4.5 Wool 4Sample 3 Color Change 2.5 Color Staining Acetate 4.5 Cotton 4.5 Nylon4.5 Polyester 3.5 Acrylic 4.5 Wool 4

In a further aspect of the present invention, the nanoparticle basedinks are present in a carrier, the nature of which is well known tothose having ordinary skill in the art. For many applications, thecarrier will be a polymer, typically a thermosetting or thermoplasticpolymer, with the latter being the more common. Examples of suitablethermosetting and thermoplastic polymers are disclosed in the cited U.S.patents and patent applications, assigned to Kimberly-Clark Worldwide,Inc., cited above. One suitable application is the incorporation ofnanoparticle into a polymer coating of a heat transfer product, such asis used for transferring graphic images onto clothing.

This invention is further illustrated by the following examples, whichare not to be construed in any way as imposing limitations upon thescope thereof. On the contrary, it is to be clearly understood thatresort may be had to various other embodiments, modifications, andequivalents thereof which, after reading the description herein, maysuggest themselves to those skilled in the art without departing fromthe spirit of the present invention. For example, it is to be understoodthat the amounts of reagents used in the following examples areapproximate and that those skilled in the art might vary these amountsand ratios without departing from the spirit of the invention. In theExamples, all parts are parts by weight unless stated otherwise.

EXAMPLES Example 1 Preparation of Polyelectrolyte-Magenta Dye-CoatedSilica Nanoparticles

A charged polymer-dye solution was first prepared as follows. A 20 mLsample of 10⁻² M poly(butyl acrylate-methacryloxyethyl trimethylammoniumbromide charged polymer was stirred while a solution of 0.06 g of acidred 52 (AR52) was added at room temperature. This solution was stirredfor 20 min. The charged polymer-dye solution prepared in this fashionwas then added to a suspension of 0.1% w/w colloidal silica (preparedfrom commercially available SNOWTEX™ C) which also contained 0.5 M NaCl.After this mixture was stirred for 20 min, the mixture was centrifuged(10,000 g) and the resulting magenta-colored powder was washed withwater 3 times and centrifuged each time. The magenta powder from thisexperiment was suspended in water and placed in a dialysis bag overnight(ca. 16 h), with water as the partition. No dye was observed to diffuseout of the bag in this dialysis experiment.

Example 2 Preparation of a Polyelectrolyte Coated Silica Nanoparticles

To a stirred suspension of 0.1% w/w colloidal silica (SNOWTEX™ C) in a0.5 M salt solution was slowly added a 0.01 M charged polymer solution,comprising polybutyl acrylate-methacryloxyethyl trimethylammoniumbromide. This mixture was centrifuged (10,000 g) and the resultingwashed with water 3 times. This reaction generated a white powdercomprising a charged polymer layered nanoparticle.

Example 3 Dialysis Control Experiment

To examine a control dialysis experiment to compare with the results inExample 1, a solution containing only Acid Red 52 dye (AR52) was placedin a dialysis bag overnight with water as a partition. In contrast tothe nanoparticle suspension dialysis experiment in Example 1, dye wasobserved to dialyze out of the bag overnight (ca. 16 h) in this control.

Example 4 Preparation of Rhodamine B-Coated Silica Nanoparticles

A 0.02 g sample of Rhodamine B dye was added to 40 mL of a 20% w/wsuspension of colloidal silica (SNOWTEX™ C). This composition wasstirred for 20 min after which the resulting mixture was placed in adialysis bag with water as a partition. After 16 hr, all the color ofthe Rhodamine B dye was still in the dialysis bag. This experimentclearly demonstrates that the positively-charged Rhodamine B dye istightly bound to the highly negatively charged silica nanoparticle. Asuspension of the Rhodamine B-layered silica nanoparticle prepared inthis fashion exhibited an absorption maximum (λ_(max)) at 556 nm(nanometers). This absorption maximum constitutes a 2 nm shift from the554 nm λ_(max) of a solution of Rhodamine B dye that is not layered ontothe surface of silica nanoparticles. A 40% wt/wt aqueous suspension ofsilica nanoparticles with Rhodamine B adsorbed has been successfullyinkjetted onto a fabric.

Example 5 Reaction of Acid Red 52 with Silica Nanoparticles

A 0.02 g sample of Acid Red 52 (AR52) dye was added to 40 mL of a 20%w/w suspension of colloidal silica (SNOWTEX™ C). This composition wasstirred for 20 min after which the resulting mixture was placed in adialysis bag with water as a partition. After 16 hr, color from the AR52dye was in the beaker, not in the dialysis bag. The absorption spectrumof a mixture AR52 and colloidal silica exhibited an absorption maximum(λ_(max)) at 565 nm (nanometers), identical to the 565 nm λ_(max) of asolution of AR52 dye alone. These experiments clearly demonstrate thatthe negatively-charged AR52 dye was not associated with the highlynegatively charged silica nanoparticle.

Example 6 Preparation of Highly Loaded Polyelectrolyte-Dye-Coated SilicaNanoparticles

A charged polymer-dye solution was prepared by stirring a 20 mL sampleof 10⁻² M poly(butyl acrylate-methacryloxyethyl trimethylammoniumbromide charged polymer while a solution of 0.24 g of acid red 52 (AR52)was added at room temperature. This solution was stirred for 20 min. Thecharged polymer-dye solution prepared in this fashion was then added toa suspension of 0.1% w/w colloidal silica (prepared from commerciallyavailable SNOWTEX™ C). After this mixture was stirred for 40 min, it wascentrifuged (10,000 g) and the resulting, magenta-colored powder waswashed with water 3 times and centrifuged each time. The magenta powderfrom this experiment was significantly darker than that obtained fromExample 1.

Example 7 Preparation of Polyelectrolyte-Yellow Dye-Coated SilicaNanoparticles

A charged polymer-dye solution was first prepared as follows. A 250 mLsample of 10⁻² M poly(butyl acrylate-methacryloxyethyl trimethylammoniumbromide charged polymer was stirred while a 0.30-g sample of CIBACRON®Yellow P-6GS was added at room temperature. This solution was stirredfor 20 min. The charged polymer-dye solution prepared in this fashionwas then added to 12.5 mL of a 20% suspension of colloidal silica(SNOWTEX™ C) which also contained 0.5 M NaCl. After this mixture wasstirred for 20 min, the mixture was centrifuged (10,000 g) and theresulting yellow-colored powder was washed with water 3 times andcentrifuged each time. The yellow powder from this experiment wassuspended in water and placed in 2 dialysis bags overnight (ca. 16 h)with water as the partition. A trace of yellow dye was observed to comeout of the bag in this dialysis experiment.

Example 8 Preparation of Polyelectrolyte-Cyan Dye-Coated SilicaNanoparticles

A charged polymer-dye solution was first prepared as follows. A 250 mLsample of 10⁻² M poly(butyl acrylate-methacryloxyethyl trimethylammoniumbromide charged polymer was stirred while a 0.49-g sample of copperphthalocyanine tetrasulfonic acid was added at room temperature. Thissolution was stirred for 20 min. The charged polymer-dye solutionprepared in this fashion was then added to 12.5 mL of a 20% wt/wtsuspension of colloidal silica (SNOWTEX™ C) which also contained 0.5 MNaCl. After this mixture was stirred for 20 min, the mixture wascentrifuged (10,000 g) and the resulting cyan-colored powder was washedwith water 3 times and centrifuged each time. The cyan powder from thisexperiment was suspended in water and placed in 2 dialysis bagsovernight (ca. 16 h) with water as the partition. A trace of cyan dyewas observed to come out of the bag in this dialysis experiment.

Example 9 Addition of a Second Polyelectrolyte Layer on Magenta SilicaNanoparticles

The suspension of magenta nanoparticles from the dialysis bag of Example1 was placed in an Erlenmeyer flask and stirred. To this solution wasadded a sufficient amount of poly(styrene sulfonic acid), sodium salt asa 10⁻² M solution in deionized water to coat the particle. Afterstirring this mixture for 20 min, the sample was placed in a newdialysis bag overnight (ca. 16 h) with water as the partition to removeany unassociated poly(styrene sulfonic acid).

Example 10 Addition of a Third Polyelectrolyte Layer on Magenta SilicaNanoparticles

A charged polymer-dye solution was prepared by stirring a 20 mL sampleof 10⁻² M poly(butyl acrylate-methacryloxyethyl trimethylammoniumbromide charged polymer while a solution of 0.24 g of acid red 52 (AR52)was added at room temperature. This solution was stirred for 20 min. Thecharged polymer-dye solution prepared in this fashion was then added toa stirred suspension of magenta nanoparticles from the dialysis bag ofExample 9 that had been removed from the bag and placed in an Erlenmeyerflask. After stirring this mixture for 20 min, the sample was placed ina new dialysis bag overnight (ca. 16 h) with water as the partition toremove any unassociated charged polymer-dye.

Example 11 Spray Coating Fabric with Magenta Silica Nanoparticles

The dialyzed suspension of magenta nanoparticles from Example 10 wassprayed onto a series of fabrics using a PREVAL® Sprayer (PrecisionValve Corporation, New York), until the fabric appeared visibly coatedwith the spray. A mask or stencil comprising the trademark design of theKimberly-Clark Worldwide Corporation allowed this design to be imprintedon the fabric. In a second series of experiments, a dialyzed suspensionof magenta nanoparticles from Example 10 to which 2 drops (in 50 mL ofsuspension) of TRITON® X-100 had been added, to allow better coating ofthe fabric fibers. In both sets of experiments, chiffon, cotton poplin,Georgette, and silk were employed as fabric substrates.

Example 12 Ink Jetting Cotton Fabric with Magenta Silica Nanoparticles

A suspension of 0.01% wt/wt silica (SNOWTEX™ C) was coated with 0.01Mcharged polymer dye of acid red 52 (AR52) as described in Example 6. Thesuspension was dialyzed at a pH of 8.5. To the resultant aqueoussuspension was added 1,3-propanediol (ca. 3% wt/wt), although moststandard co-solvent and surfactant additives could be used. This inkmixture was stirred for 20 min, and then syringed into an HP Margaritainkjet cartridge. This ink composition was inkjet printed onto uncoatedcotton fabric using a Colorspan DMII wide format printer. The suspensionink jetted well onto the cotton fabric to give a magenta print.

Example 13 Adsorption of a Non-Charged Polymer onto Silica Nanoparticles

A suspension of colloidal silica (SNOWTEX™ C), diluted with deionizedwater to 1% wt/wt silica nanoparticles in water, was treated with a 0.1%wt/wt solution ofpoly[N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine-co-2,4-dichloro-6-morpholino-1,3,5-triazine](abbreviated PPMT, Aldrich Chemical Co. no. 41,324-0, CAS registry no.82451-48-7). The zeta potential was measured before and after additionof the polymer, and found to change from −36 mV before addition, to +70mV after addition. Zeta potential measurements were taken using aZetapals Instrument (Brookhaven Instrument Corporation, Holtsville,N.Y.), by adding 1-3 drops of sample into a cuvet containing 1 mM KClsolution, using the instrument's default functions preset for aqueoussolutions. This mixture was stirred for 40 minutes and then dialyzedovernight against pH 9, using 2000 molecular weight dialysis bags. Thisdramatic increase in measured zeta potential upon the addition of thePPMT polymer solution indicates the absorption of the non-chargedpolymer to the silica nanoparticle. This example also illustrates theincorporation of a UV stabilizer into a nanoparticle, as PPMT is astrong absorber of UV radiation.

Example 14 Adsorption of a Non-Charged Polymer onto Silica Nanoparticlesat High Concentrations

A 50-mL sample of 20% wt/wt suspension of colloidal silica (SNOWTEX™ C)in water was treated with 10 mL of 0.1 N HCl solution to achieve asolution pH of 4. The zeta potential was observed to change slightlyfrom −32 mV to −30 mV upon treatment with HCl. A solid sample ofpoly[N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine-co-2,4-dichloro-6-morpholino-1,3,5-triazine](PPMT, Aldrich Chemical Co. no. 41,324-0, CAS registry no. 8245148-7)was added directly to the suspension of colloidal silica and stirred. Aclear suspension of particles was obtained, which exhibited a zetapotential of +35 mV, indicating the PPMT polymer coating on the silicaparticle.

Example 15 Adsorption of a Non-Charged Polymer onto Magenta Dye-CoatedSilica Nanoparticles, Followed by Protonation, to Achieve a High ZetaPotential Nanoparticle

A 0.2 g sample of Rhodamine B dye was added to 20 mL of a 20% w/wsuspension of colloidal silica (SNOWTEX™ C), at pH 8.5. This mixture wasstirred for about 20 min after which about 5 mL of dilute HCl was addedto the suspension until the pH was reduced to about 3. A 0.2 g-sample ofpoly[N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine-co-2,4-dichloro-6-morpholino-1,3,5-triazine](PPMT, Aldrich Chemical Co. no. 41,324-0, CAS registry no. 8245148-7)was added to this suspension of silica/Rhodamine B nanoparticles at pH3, with stirring, whereupon the pH increased to about 7.3. Additionaldilute HCl was added until the pH was reduced to 4.1. The zeta potentialof the particles in this suspension was measured to be +35 mV after HCladdition, indicating protonation of the PPMT polymer.

Example 16 Printing Cotton Fabric with a High Zeta Potential MagentaNanoparticles

A 3 inch by 1 inch swatch of plain, untreated cotton fabric (with astreaming potential of −23 mV) was dipped into the suspension of magentananoparticles prepared in Example 13 for about 10 sec, rinsed in coldwater, and then dried under vacuum at ambient temperature. A smaller(about 1 inch by 2 inch) piece of colored fabric was cut from thissample and subjected to the AATCC 61-2A accelerated laundering test, bythe ACTS Testing Labs (Buffalo, N.Y.). This test for evaluatingcolorfastness should show color change similar to that produced by fivecommercial launderings at 38±3° C. (100±5° F.) or by five home machinelaunderings at medium or warm setting in this same temperature range.The fabric sample was washed in 150 mL of water at 49° C. (120° F.) with0.25% SYNTHRAPOL™ detergent, along with 50 (0.6 cm) steel ball bearings.Wash time was 45 min, in a canister being rotated at a rate of 40 rpm.The laundered sample was then washed with water and dried, and the ΔE*color change was measured as described above, as compared to anunlaundered sample. The ΔE* value was measured to be 5.3 for thissample, on a scale where a color change ΔE* value of 5 or lessrepresents a color change that a human eye will not be able to detect ascompared with the control sample. This measurement indicates that a zetapotential of +35 mV for the particle suspension is sufficient for thisfabric with a streaming potential of −23 mV, to achieve good adhesionand durability.

Example 17 Adsorption of a Non-Charged Polymer onto Cyan Dye-CoatedSilica Nanoparticles, Followed by Protonation, to Achieve a High ZetaPotential Nanoparticle

A 0.2 g sample of Victoria Blue BO cyan dye (Aldrich Chemical Co.,Milwaukee, Wis.) was added to 50 mL of a 20% w/w suspension of colloidalsilica (SNOWTEX™ C), at pH 8.5. This mixture was stirred for about 20min after which dilute HCl was added to the suspension until the pH wasreduced to about 4.5. A 0.30 g-sample ofpoly[N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine-co-2,4-dichloro-6-morpholino-1,3,5-triazine](Aldrich Chemical Co. no. 41,324-0, CAS registry no. 82451-48-7;abbreviated PPMT) was added to this suspension of silica/Victoria BlueBO nanoparticles, whereupon the pH increased to about 7.5. About 10 mLof additional dilute HCl was added until the pH was reduced to about4.5. The zeta potential of this suspension was measured to be +30 mVafter HCl addition, indicating protonation of the PPMT polymer.

Example 18 Printing Cotton Fabric with a High Zeta Potential CyanNanoparticles

A 3 inch by 1 inch swatch of plain, untreated cotton fabric (with astreaming potential of −23 mV) was soaked with the suspension of cyannanoparticles prepared in Example 17, rinsed in cold water, and thendried under vacuum at ambient temperature. A smaller (about 1 inch by0.5 inch) piece of colored fabric was cut from this sample and subjectedto the AATCC 61-2A accelerated laundering test. The fabric sample waswashed in 150 mL of water at 49° C. (120° F.) with 0.25% SYNTHRAPOL™detergent, along with 50 (0.6 cm) steel ball bearings. Wash time was 45min, in a canister being rotated at a rate of 40 rpm. The launderedsample was then washed with water and dried, and the ΔE* color changewas measured as compared to an unlaundered sample. The ΔE* value wasmeasured to be 1.3 for this sample, on a scale where a color change ΔE*value of 5 or less represents a color change that a human eye will notbe able to detect as compared with the control sample. This measurementindicates that a zeta potential of +30 mV for the particle suspension issufficient for this fabric with a streaming potential of −23 mV, toachieve strong adhesion and high durability.

Example 19 Coating Melamine Resin Particles with Yellow Colorant and aCharged Polymer

A 10 mL sample of 0.9 micron (μm) particles of poly(melamineformaldehyde) (Microparticles GmbH, Berlin) was prepared as a 2.5% wt/wtsample in water was titrated with 0.1 N HCl solution until the pH waslowered to 4.5. The change in pH of the suspension was monitored byperforming the titration while the pH electrode was immersed therein. AtpH 4.5, the zeta potential of the suspension was measured at +33 mV.This suspension was stirred while 0.1 g of yellow dye (CIBACRON® YellowP-6GS) was added, after which the zeta potential was measured at −21 mV(at pH 4.5). After an additional 20 min of stirring, the PE(+) chargedpolymer, polyethyleneimine permethyl perbromide (Polysciences, Inc.,Warrington, Pa., 1800 Mw molecular weight), was added (10 mL of a 10⁻² Msolution), after which the zeta potential was measured at +33 mV (at pH4.5). Zeta potential measurements were taken using a Zetapals Instrument(Brookhaven Instrument Corporation, Holtsville, N.Y.), by adding 1-3drops of sample into a cuvet containing 1 mM KCl solution, using theinstrument's default functions preset for aqueous solutions. ThisExample indicates how poly(melamine formaldehyde) particles can becoated with a dye followed by a PE(+) charged polymer coating in orderto achieve a positive nanoparticle zeta potential which results instrong adhesion to fabric with a negative streaming potential, andthereby providing high durability of print.

Example 20 Coating Melamine Resin Particles with Multiple Colorant andPolyelectrolyte Coatings

Melamine resin particles (poly(melamine formaldehyde)) (MicroparticlesGmbH, Berlin) were suspended in water and titrated with 0.1 N HClsolution until the pH was lowered to 3.7. This suspension was stirredwith rhodamine B dye at pH 3.7 to coat the particles, after which thezeta potential of the suspension was measured at +32 mV. This suspensionwas then stirred while the yellow dye CIBACRON® Yellow P-6GS was added,after which the zeta potential was measured at −24 mV, and thesuspension was characterized by an orange color. The PE(+) chargedpolymer, polyethyleneimine permethyl perbromide (Polysciences, Inc.,Warrington, Pa., 1800 Mw molecular weight) was then added, after whichthe zeta potential was measured at +28 mV. After about 1 hr, the orangeparticles had settled to the bottom of the flask, indicating that thedyes were adsorbed onto the poly(melamine formaldehyde) particles, andwere not in solution.

Example 21 Coating Melamine Resin Particles with Multiple Colorant andCharged Polymer Coatings

Melamine resin particles (poly(melamine formaldehyde)) (MicroparticlesGmbH, Berlin) were suspended in water and titrated with 0.1 N HClsolution until the pH was lowered to 3.7. This suspension was stirredwith Rhodamine B dye at this pH to coat the particles, after which thezeta potential of the particles in suspension was measured at +32 mV.This suspension was then stirred while Acid Red 52 dye was added,forming a deep magenta color, after which the zeta potential wasmeasured at −20 mV. Additional Acid Red 52 was added, forming asuspension with a deeper magenta color, and characterized by a zetapotential of −23 mV. To this suspension was added the polytriazinecopolymer,poly[N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine-co-2,4-dichloro-6-morpholino-1,3,5-triazine](Aldrich Chemical Co. No. 41,324-0, CAS registry no. 82451-48-7;abbreviated PPMT), followed by acidification with 0.1 N HCl, whereuponthe zeta potential was found to be +44 mV.

Example 22 Coating Melamine Resin Particles with Multiple Colorant andCharged Polymer Coatings

Melamine resin particles (poly(melamine formaldehyde)) (MicroparticlesGmbH, Berlin) were suspended in water and titrated with 0.1 N HClsolution until the pH was lowered to 3.7. This suspension was stirredwith Nile Blue stain at this pH to coat the particles, after which thezeta potential of the suspension was measured at +10 mV, and thesuspension was pale blue in color. This suspension was then stirredwhile CIBACRON® Yellow P-6GS dye was added, forming a green suspensioncolor, after which the zeta potential was measured at −30 mV. To thissuspension was addedpoly[N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)-1,6-hexanediamine-co-2,4-dichloro-6-morpholino-1,3,5-triazine](Aldrich Chemical Co.), followed by acidification with 0.1 N HCl, tobring the pH back to 3.7, whereupon the zeta potential was found to be+44 mV. After about 1 hr, the green particles had settled to the bottomof the flask, showing adsorption of the dyes to the particle surface.

Example 23 Preparation of a Polyelectrolyte Coated Alumina Nanoparticles

A sample of ALUMINASOL™ 100 (Nissan Chemical America Corporation) wasdiluted from 10% to 1% wt/wt in 1 mM aqueous KCl. The zeta potential ofthis suspension was measured at +63 mV. This suspension was stirredwhile 20 ml of a 0.1 M solution of poly(vinyl sulfonic acid, sodiumsalt) (1800 Mw molecular weight) was added. The suspension was stirredfor another 40 min, after which time the zeta potential was measured tobe +10 mV, indicating the alumina sol can serve as a template.

Example 24 Preparation of Polyelectrolyte-Dye-Coated SilicaNanoparticles Using Alternately Charged Polyelectrolytes, and ZetaPotential Measurements of the Resulting Particles

A polyelectrolyte-dye solution was first prepared as follows. A 20 mLsample of 10⁻² M polyethyleneimine permethylated perbromidepolyelectrolyte (1800 MW) was stirred while a 0.022-gram sample of acidred 52 (AR52) was added at room temperature. Thus, 0.2 mmol of PE(+)polyethyleneimine permethylated perbromide was treated with 0.04 mmol ofdye, meaning that 20% of the sites are occupied with the dye. If thisresulting solution is dialyzed with 2000 MW cut off dialysis bags, nodye was observed outside the bag after 16 hr of dialysis, indicating astrong dye-charged polymer complex had formed. This 20 mL sample ofpolyelectrolyte-dye solution was added to 200 mL of a 0.01% wt/wtsuspension of 9-14 nm silica nanoparticles at pH 8.5 and 1M in NaCl. Theresulting suspension was stirred for 40 mins at room temperature. Thissuspension was then stirred overnight against a pH 8.5/1M NaCl solutionusing 2000 MW cut off dialysis bags. The contents of the dialysis bagwere then treated with 20 mL of a 10⁻² M poly(vinyl sulfonic acid,sodium salt) solution (1800 MW) for 40 min at room temperature. Theresulting suspension was then dialyzed overnight, as before, with a 2000MW cut off dialysis bag. Both layering steps could then be repeated ifdesired to build up layers on the silica nanoparticle. In addition, thisprocess can be performed with up to 1% wt/wt silica nanoparticles and0.1 M PE(+) polyethyleneimine permethylated perbromide polyelectrolyte.Zeta potentials were measured for the nanoparticle itself, and followingsubsequent layering of polyelectrolyte(+)-dye, (void)polyelectrolyte(−), and polyelectrolyte(+)-dye, as shown in Table 2. Thezeta potential data in Table 2 reflect measurements using magenta,yellow, and cyan dyes in separate experiments, although clearlydifferent dyes can be used on the same nanoparticle to providespecifically tailored colors.

Example 25 Effect of Nanoparticle Zeta Potential on Durability

The AATCC 61-2A test for evaluating colorfastness was used to evaluateand compare the durability of various colored nanoparticles on a singlefabric. The AATCC 61-2A test shows color change comparable to fivecommercial launderings at 38±3° C. (100±5° F.) or by five home machinelaunderings at medium or warm setting in this temperature range. Acotton sample printed with various colored nanoparticles was washed in150 mL of water at 49° C. (120° F.) with 0.25% SYNTHRAPOL™ detergent,along with 50 (0.6 cm) steel ball bearings. Wash time was 45 min, in acanister being rotated at a rate of 40 rpm. The laundered sample wasthen washed with water and dried, and the loss of color, ΔE* wasmeasured according to AATCC 61-2A. Samples that were measured with a ΔE*on a scale where a color change ΔE* value of 5 or less represents acolor change that a human eye will not be able to detect as comparedwith the control sample. The grade ratings were determined through useof the AATCC Gray Scales for Color Change and Staining. Table 4 recordsthe results of the AATCC 61-2A accelerated laundering test for variousfabric samples and colorants of the present invention. In Table 4, thefollowing abbreviations are used: SNC is SNOWTEX™ C; PE(+) ispolyethylenimine, permethylated, perbromide (MW=1800, Polysciences,Warrington, Pa.); PE(−) is poly(vinylsulfonic acid, sodium salt)MW=2000, Polysciences, Warrington, Pa.); AR52 is acid red 52 dye; RhB isrhodamine B dye; MR is melamine formaldehyde particles, comprisingpoly(melamine formaldehyde) resin. The nanoparticle core and the orderof layering is indicated by the sequence as presented in the table. Thedramatic differences shown in this table indicate the importance of zetapotential of the nanoparticle in providing enhanced durability.

TABLE 4 Effect of Nanoparticle Zeta Potential on Durability Measured byAATCC-61-2A Zeta Potential ΔE*, Loss of Color on Nanoparticle (mV)Laundering (Cotton) SNC/PE(+)-AR52 −28 49.0 SNC/PE(+)-AR52/PE(−)/ −2443.8 PE(+)-AR52 SNC/PE(+)/PE(−)-RhB/ −20 37.4 PE(+) SNC/RhB −10 12.0MR/RhB +42 5.7 MR/RhB +78 1.3

Example 26 Colorfastness Testing of Fabrics Printed with NanoparticleInk

A variety of fabrics were printed using nanoparticle inks of the presentinvention, and colorfastness and printability tests were conducted onthe resulting printed fabrics. Table 5 records the data obtained inthese tests. The particular colorfastness tests used are indicated,where AATCC is the American Association of Textile Chemists andColorists, and ACTS is the ACTS Testing Laboratory, Buffalo, N.Y. Thesetests were performed at the ACTS Testing Laboratory on fabrics printedwith a suspension of magenta melamine resin nanoparticles. Thecolorfastness gray scale method used to judge these tests ranges from 1to 5, with 3 and higher deemed passing (no detectable change).

TABLE 5 Colorfastness Testing of Fabrics Printed with Nanoparticle InkTest and Method Cotton Nylon Silk Printability Pass Pass PassColorfastness to Water (AATCC 107) 4 3.5 4 Colorfastness to Perspiration(AATCC 15) 5 4 5 Colorfastness to Accelerated Laundering 3.5 3.5 3.5(AATCC 61-2A) Colorfastness to Chlorine Bleach 3.5 3.5 3.5 (ACTS MethodTX-006) Colorfastness to Non-Chlorine Bleach 4.5 4.5 3.5 (ACTS MethodTX-011) Colorfastness to Crocking (AATCC 8) 4 3 3.5

Example 27 Comparison of Colorfastness Testing of Fabrics Printed withStandard Inks Versus Nanoparticle Inks

In this test, both coated cotton and uncoated cotton were utilized assubstrates to compare colorfastness of the nanoparticle ink of thepresent invention with standard inks that do not employ nanoparticletechnology. The coated cotton was post treated with steam, followed byrinsing, and this “improved” substrate was treated with a standardmagenta ink. The standard colorant treatment was a Kimberly-Clark mediumred (magenta) ink, prepared using the following formulation in Table 6.

TABLE 6 Formulation for Standard Magenta Ink for Comparison Testing InkComponent Weight % Supplier DI water 82.0 — Versene ® 100XL 0.6 DowChemical Co., Midland Michigan EDTA•2Na 0.3 Dow Chemical Co., MidlandMichigan N-methylmorph- 3.0 Aldrich Chemical Co., Milwaukee,oline-N-oxide Wisconsin Glycerine 3.5 Aldrich Chemical Co., Milwaukee,Wisconsin PEG-400 5.0 Aldrich Chemical Co., Milwaukee, WisconsinProxel ® GXL 0.3 Zenneca Corp., Wilmington, Delaware Cobratec ® Soln 0.3PMC Speciality Group, Cincinnati, Ohio Surfynol ® 504 0.1 Air Products,Allentown, Pennsylvania Surfynol ® 465 0.2 Air Products, Allentown,Pennsylvania Reactive Dye RM 4.7 Ciba Specialty Chemicals Corp., 7034,Cibacron ® Highpoint, North Carolina Red P-6B Total 100.0

The nanoparticle colorant was a suspension of magenta melamine resinnanoparticles, and was applied to an uncoated cotton fabric thatemployed no post treatment. Table 7 records the results of these tests,which reveal that even unimproved substrates with nanoparticle inksperform better than improved substrates with standard inks. Thecolorfastness gray scale method used to judge these tests ranges from 1to 5, with 3 and higher deemed passing (no detectable change).

TABLE 7 Comparison of Colorfastness Testing of Fabrics Printed withStandard Ink versus Nanoparticle Ink Standard Nanoparticle Test andMethod Ink Ink Substrate coated cotton uncoated cotton Post treatmentsteam + rinse None Printability Pass Pass Colorfastness to Water (AATCC107) 4.5 4.5 Colorfastness to Perspiration (AATCC 15) 4.5 4.5Colorfastness to Accelerated Laundering 1.5 3 (AATCC 61-2A)Colorfastness to Chlorine Bleach 4.5 4.5 (ACTS Method TX-006)Colorfastness to Non-Chlorine Bleach 3 4.5 (ACTS Method TX-011)Colorfastness to Crocking (AATCC 8) N/A 4

Example 28 Effect of Fabric on the Durability of Nanoparticle Inks

The durability of the inks of the present invention when applied tovarious fabrics was tested, in order to ascertain the effect of thechoice of fabric. As shown in Table 8 below, all the fabrics tested weremeasured as having negative streaming potentials, while the melamineresin nanoparticles were measured with a positive zeta potential. Both amagenta melamine nanoparticle, and a cyan melamine resin nanoparticle ofthe present invention were employed in this study. Durability ismeasured as both colorfastness to accelerated laundering (AATCC 61-2Atest) and as colorfastness to crocking (AATCC 8). The colorfastness grayscale method used to judge these tests ranges from 1 to 5, with 3 andhigher deemed passing (no detectable change).

TABLE 8 Effect of Fabric on the Durability of Nanoparticle InksDurability Streaming Accelerated Laundering Colorfastness to Potential(AATCC 61-2A) Crocking (AATCC 8) Fabric (mV) Magenta Cyan Magenta CyanCotton −21 3.5 3 4 4.5 Nylon −32 3.5 3.5 3 3 Silk −26 3.5 3.5 3.5 4Polyester −20 — 3.5 — 3.5

Example 29 Preparation of Colored Nanoparticles Using Different Dyes toObtain Unusual Colors

One feature of the present invention is the ability to preparenanoparticle colorants with unusual or hard-to-obtain colors. Thus, whenadsorbing each layer onto the nanoparticle template, each chargedpolymer layer can employ a different dye for fine tuning colors. Thus,silica nanoparticles were coated with a PE(+)/Acid Red 52 layer to yieldmagenta nanoparticles, which were subsequently coated with a PE(+)/cyanlayer to afford lilac colored nanoparticles. The cyan colorant used wascopper phthalocyanine, tetrasulfonic acid, sodium salt. Thus, by mixinglayers of color in this fashion, a uniform ink/dye system of unusualcolor can be prepared. This result is to be contrasted to simplemixtures of colorants or dyes that would not result in a similarly truecolor, but rather the hues of the component dyes.

Example 30 Preparation and Utility of a Surface Modifying Ink Jet InkContaining Nanoparticles

Silica nanoparticles (SNOWTEX™ C, Nissan Chemical) were treated withpolyvinylpyrrolidone (Mw 10,000) in an aqueous suspension at pH 8.5 and1 M in NaCl, for a period of 2 hours. The zeta potential of thenanoparticles changed from −34 mV to −10 mV and the nanoparticle sizechanged from 10 nm to 25 m as a direct result of the adsorption of thepolyvinylpyrrolidone onto the silica nanoparticle. Excesspolyvinylpyrrolidone was removed by dialysis against a 1 M NaCl solutionat pH 8.5 for 16 hours, with a 20,000 MW cut off. The resultingsuspension of modified nanoparticles was drawn down onto a sheet ofNeenah bond paper. When this paper was allowed to dry, it was observedto have a high gloss. This example demonstrates that nanoparticletechnology may be used in an inkjet system for surface modification of asubstrate. This example differs from others in this disclosure in thatthe ink used for surface modification is not colored.

Further discussion of nanoparticles may be found in U.S. patentapplication Ser. No. ______, entitled, “Recording Medium withNanoparticles and Methods of Making the Same”, by R. S. Nohr, J. G.MacDonald and B. Kronberg, filed contemporaneously herewith.

It should be understood, of course, that the foregoing relates only tocertain embodiments of the present invention and that numerousmodifications or alterations may be made therein without departing fromthe spirit and the scope of the invention.

1. A recording medium comprising a nanoparticle having a size of lessthan about 1,000 nanometers and comprising: a polymeric core having apositive or a negative zeta potential; a first charged polymer layerdisposed on the core and having a zeta potential different from the zetapotential of the core; at least one successive charged polymer layerdisposed on the first charged polymer layer, wherein the zeta potentialof the at least one successive charged polymer layer is different fromthat of the charged polymer layer adjacent thereto; and a carrier.
 2. Aprinting process comprising ejecting a recording medium in the form ofdroplets from an orifice in accordance with a recording signal to forman image on a substrate, the recording medium comprising: a nanoparticlehaving a size of less than about 1,000 nanometers and comprising apolymeric material having at least one colorant disposed within thepolymeric material; and a carrier.
 3. The printing process of claim 2,wherein the process is an ink-jet process.
 4. The printing process ofclaim 2, wherein the substrate is a textile, a cellulose, a paper, aceramic, a polymer, a wood, or a glass.
 5. A printing process comprisingejecting a recording medium in the form of droplets from an orifice inaccordance with a recording signal to form an image on a substrate, therecording medium comprising: a nanoparticle having a size of less thanabout 1,000 nanometers and comprising a polymeric material having atleast one colorant disposed within the polymeric material; a surfacemodifying layer disposed on and substantially covering the nanoparticle;and a carrier.
 6. The printing process of claim 5, wherein the surfacemodifying layer comprises an agent selected from polyvinyl alcohol,polyvinyl pyrrolidone, polyacrylic acid, polysiloxane, polysiloxanepolyethylene oxide copolymer, polysiloxane polypropylene oxidecopolymer, linear dextrins, cyclodextrins, chitosans, or combinationsthereof.
 7. A method of making a recording medium comprising: providinga plurality of particles comprising a polymeric core having an agentdisposed within the polymer and at least one charged polymer layerdisposed on and substantially covering the core; providing a carrier;and admixing the particles and the carrier.
 8. A method of making arecording medium comprising: providing a plurality of nanoparticleshaving a size of less than about 1,000 nanometers and comprising apolymeric material having at least one colorant disposed within thepolymeric material; providing a carrier; and admixing the plurality ofnanoparticles and the carrier.
 9. A method of making a recording mediumcomprising: providing a plurality of nanoparticles having a size of lessthan about 1000 nanometers comprising a polymeric core having an agentdisposed within the polymer and at least one charged polymer layer;providing a carrier; and admixing the plurality of nanoparticles and thecarrier.
 10. A method of making a recording medium comprising: providinga plurality of nanoparticles having a size of less than about 1000nanometers comprising a polymeric core having at least one colorantdisposed within the polymer and a protective coating disposed on andsubstantially covering the nanoparticle; providing a carrier; andadmixing the nanoparticle and the carrier.
 11. A method of making arecording medium comprising: providing a plurality of nanoparticleshaving a size of less than about 1,000 nanometers and comprising apolymeric core having a positive or a negative zeta potential, a firstcharged polymer layer disposed on the core and having a zeta potentialopposite the zeta potential of the core and at least one successivecharged polymer layer disposed on the first charged polymer layer,wherein the zeta potential of the at least one successive chargedpolymer layer is opposite that of the charged polymer layer adjacentthereto; providing a carrier; and admixing the plurality ofnanoparticles and the carrier.
 12. A method of making a recording mediumcomprising: providing a first solution comprising at least one polymer,at least one colorant, and a first solvent; combining the first solutionwith a second solution comprising a second solvent in which the firstsolvent is substantially immiscible; emulsifying the first and secondsolutions to produce a polymeric particle having the colorant disposedtherein; and suspending the resulting particle in a liquid medium. 13.The method of making a recording medium of claim 12, wherein thecolorant is disposed within the polymeric particle.
 14. The method ofmaking a recording medium of claim 12, further comprising the step ofisolating the particle.
 15. The method of making a recording medium ofclaim 12, wherein the at least one colorant comprises a dye.
 16. Themethod of making a recording medium of claim 12, wherein the at leastone colorant is present in the polymeric particle from about 1 percentby weight to about 30 percent by weight.
 17. The method of making arecording medium of claim 12, wherein the polymer comprises an organicpolymer, an inorganic polymer, semi-organic polymer, semi-inorganicpolymer, an organometallic polymer, or a combination thereof.
 18. Themethod of making a recording medium of claim 12, wherein the polymercomprises polyisoprene, polybutadiene, poly(acrylonitrile-co-butadiene),poly(α-methyl styrene), poly(vinyl acetate), poly(vinyl alcohol),polystyrene, polyethylene, polypropylene, polymethylmethacrylate, or acombination thereof.
 19. The method of making a recording medium ofclaim 12, wherein polymer particle has a size of less than about 1,000nanometers.
 20. The method of making a recording medium of claim 12,wherein polymer particle has a size of less than about 400 nanometers.21. The method of making a recording medium of claim 12, wherein thepolymer particle has a size of less than about 100 nm.
 22. The method ofmaking a recording medium of claim 12, wherein the nanoparticle has azeta potential of about +20 mV or greater.
 23. The method of making arecording medium of claim 12, wherein the nanoparticle has a zetapotential of about +50 mV or greater.